JP2024114273A - Etching method and etching apparatus - Google Patents

Abstract

To provide a technique for suppressing shape abnormalities in the side walls of recesses formed by etching.SOLUTION: An etching method includes a step (a) of etching a substrate to form a first portion of a recess in the substrate, in which the first portion includes a bottom surface and sidewalls, a step (b) of forming an ammonium fluoroborate layer in or on the sidewalls, and a step (c) of etching the bottom surface while protecting the sidewalls with the ammonium fluoroborate layer to form a second portion of the recess below the first portion.SELECTED DRAWING: Figure 3

Description

An exemplary embodiment of the present disclosure relates to an etching method and an etching apparatus.

In the manufacture of electronic devices, plasma etching of a silicon-containing film on a substrate is performed. In plasma etching, the silicon-containing film is etched using plasma generated from a processing gas. JP 2016-39309 A discloses a processing gas containing hydrogen gas, a fluorohydrocarbon gas, a fluorine-containing gas, a hydrocarbon gas, boron trichloride gas, and nitrogen gas as a processing gas used in plasma etching of a silicon-containing film. JP 2014-17406 A discloses a processing gas containing boron as a processing gas used in plasma etching of a silicon-containing film.

JP 2016-39309 A JP 2014-17406 A

This disclosure provides a technology that suppresses shape abnormalities in the sidewalls of recesses formed by etching.

In one exemplary embodiment, the etching method includes the steps of: (a) etching a substrate to form a first portion of a recess in the substrate, the first portion including a bottom surface and a sidewall; (b) forming an ammonium fluoroborate layer in or on the sidewall; and (c) etching the bottom surface while protecting the sidewall with the ammonium fluoroborate layer to form a second portion of the recess below the first portion.

According to one exemplary embodiment, a technique is provided for suppressing shape abnormalities on the sidewalls of recesses formed by etching.

FIG. 1 is a schematic diagram of a plasma processing apparatus according to an exemplary embodiment. FIG. 2 is a schematic diagram of a plasma processing apparatus according to an exemplary embodiment. FIG. 3 is a flow chart of an etching method according to one exemplary embodiment. FIG. 4 is a cross-sectional view of an example substrate to which the method of FIG. 3 may be applied. FIG. 5 is a cross-sectional view illustrating a step of an etching method according to an exemplary embodiment. FIG. 6 is a cross-sectional view illustrating a step of an etching method according to an exemplary embodiment. FIG. 7 is a cross-sectional view illustrating a step of an etching method according to an exemplary embodiment. FIG. 8 is a flowchart of the etching method according to the first modified example. FIG. 9 is a cross-sectional view showing a step of the etching method according to the first modification. FIG. 10 is a cross-sectional view showing a step of the etching method according to the first modification. FIG. 11 is a flowchart of the etching method according to the second modified example. FIG. 12 is a diagram showing a part of a flowchart of the etching method according to the second modified example. FIG. 13 is a partially enlarged cross-sectional view of an example of a substrate for evaluating the degree of shape abnormality of a recess. FIG. 14 is a graph showing an example of the results of an experiment evaluating the degree of shape abnormality of the recesses. FIG. 15 shows an example of the results of another experiment evaluating the degree of shape abnormality of the recesses. FIG. 16 shows an example of the results of another experiment evaluating the degree of shape abnormality of the recesses.

Various exemplary embodiments will be described in detail below with reference to the drawings. Note that the same or equivalent parts in each drawing will be given the same reference numerals.

Figure 1 is a diagram for explaining an example of the configuration of a plasma processing system. In one embodiment, the plasma processing system includes a plasma processing device 1 and a control unit 2. The plasma processing system is an example of a substrate processing system, and the plasma processing device 1 is an example of a substrate processing device. The plasma processing device 1 includes a plasma processing chamber 10, a substrate support unit 11, and a plasma generation unit 12. The plasma processing chamber 10 has a plasma processing space. The plasma processing chamber 10 also has at least one gas supply port for supplying at least one processing gas to the plasma processing space, and at least one gas exhaust port for exhausting gas from the plasma processing space. The gas supply port is connected to a gas supply unit 20 described later, and the gas exhaust port is connected to an exhaust system 40 described later. The substrate support unit 11 is disposed in the plasma processing space and has a substrate support surface for supporting a substrate.

The plasma generating unit 12 is configured to generate plasma from at least one processing gas supplied into the plasma processing space. The plasma formed in the plasma processing space may be capacitively coupled plasma (CCP), inductively coupled plasma (ICP), electron-cyclotron-resonance plasma (ECR plasma), helicon wave plasma (HWP), or surface wave plasma (SWP). Also, various types of plasma generating units may be used, including AC (Alternating Current) plasma generating units and DC (Direct Current) plasma generating units. In one embodiment, the AC signal (AC power) used in the AC plasma generating unit has a frequency in the range of 100 kHz to 10 GHz. Thus, AC signals include RF (Radio Frequency) signals and microwave signals. In one embodiment, the RF signal has a frequency in the range of 100 kHz to 150 MHz.

The control unit 2 processes computer-executable instructions that cause the plasma processing apparatus 1 to execute various steps described in this disclosure. The control unit 2 may be configured to control each element of the plasma processing apparatus 1 to execute various steps described herein. In one embodiment, a part or all of the control unit 2 may be included in the plasma processing apparatus 1. The control unit 2 may include a processing unit 2a1, a storage unit 2a2, and a communication interface 2a3. The control unit 2 is realized, for example, by a computer 2a. The processing unit 2a1 may be configured to perform various control operations by reading a program from the storage unit 2a2 and executing the read program. This program may be stored in the storage unit 2a2 in advance, or may be acquired via a medium when necessary. The acquired program is stored in the storage unit 2a2 and is read from the storage unit 2a2 by the processing unit 2a1 and executed. The medium may be various storage media readable by the computer 2a, or may be a communication line connected to the communication interface 2a3. The processing unit 2a1 may be a CPU (Central Processing Unit). The storage unit 2a2 may include a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disk Drive), a SSD (Solid State Drive), or a combination of these. The communication interface 2a3 may communicate with the plasma processing apparatus 1 via a communication line such as a LAN (Local Area Network).

Below, an example of the configuration of a capacitively coupled plasma processing apparatus is described as an example of the plasma processing apparatus 1. Figure 2 is a diagram for explaining an example of the configuration of a capacitively coupled plasma processing apparatus.

The capacitively coupled plasma processing apparatus 1 includes a plasma processing chamber 10, a gas supply unit 20, a power supply 30, and an exhaust system 40. The plasma processing apparatus 1 also includes a substrate support unit 11 and a gas inlet unit. The gas inlet unit is configured to introduce at least one processing gas into the plasma processing chamber 10. The gas inlet unit includes a shower head 13. The substrate support unit 11 is disposed in the plasma processing chamber 10. The shower head 13 is disposed above the substrate support unit 11. In one embodiment, the shower head 13 constitutes at least a part of the ceiling of the plasma processing chamber 10. The plasma processing chamber 10 has a plasma processing space 10s defined by the shower head 13, the sidewall 10a of the plasma processing chamber 10, and the substrate support unit 11. The plasma processing chamber 10 is grounded. The shower head 13 and the substrate support unit 11 are electrically insulated from the housing of the plasma processing chamber 10.

The substrate support 11 includes a main body 111 and a ring assembly 112. The main body 111 has a central region 111a for supporting the substrate W and an annular region 111b for supporting the ring assembly 112. A wafer is an example of a substrate W. The annular region 111b of the main body 111 surrounds the central region 111a of the main body 111 in a plan view. The substrate W is disposed on the central region 111a of the main body 111, and the ring assembly 112 is disposed on the annular region 111b of the main body 111 so as to surround the substrate W on the central region 111a of the main body 111. Therefore, the central region 111a is also called a substrate support surface for supporting the substrate W, and the annular region 111b is also called a ring support surface for supporting the ring assembly 112.

In one embodiment, the main body 111 includes a base 1110 and an electrostatic chuck 1111. The base 1110 includes a conductive member. The conductive member of the base 1110 may function as a lower electrode. The electrostatic chuck 1111 is disposed on the base 1110. The electrostatic chuck 1111 includes a ceramic member 1111a and an electrostatic electrode 1111b disposed within the ceramic member 1111a. The ceramic member 1111a has a central region 111a. In one embodiment, the ceramic member 1111a also has an annular region 111b. Note that other members surrounding the electrostatic chuck 1111, such as an annular electrostatic chuck or an annular insulating member, may have the annular region 111b. In this case, the ring assembly 112 may be disposed on the annular electrostatic chuck or the annular insulating member, or may be disposed on both the electrostatic chuck 1111 and the annular insulating member. Also, at least one RF/DC electrode coupled to an RF power source 31 and/or a DC power source 32 described later may be disposed in the ceramic member 1111a. In this case, the at least one RF/DC electrode functions as a lower electrode. When a bias RF signal and/or a DC signal described later is supplied to the at least one RF/DC electrode, the RF/DC electrode is also called a bias electrode. Note that the conductive member of the base 1110 and the at least one RF/DC electrode may function as multiple lower electrodes. Also, the electrostatic electrode 1111b may function as a lower electrode. Thus, the substrate support 11 includes at least one lower electrode.

The ring assembly 112 includes one or more annular members. In one embodiment, the one or more annular members include one or more edge rings and at least one cover ring. The edge rings are formed of a conductive or insulating material, and the cover rings are formed of an insulating material.

The substrate support 11 may also include a temperature adjustment module configured to adjust at least one of the electrostatic chuck 1111, the ring assembly 112, and the substrate to a target temperature. The temperature adjustment module may include a heater, a heat transfer medium, a flow passage 1110a, or a combination thereof. A heat transfer fluid such as brine or a gas flows through the flow passage 1110a. In one embodiment, the flow passage 1110a is formed in the base 1110, and one or more heaters are disposed in the ceramic member 1111a of the electrostatic chuck 1111. The substrate support 11 may also include a heat transfer gas supply configured to supply a heat transfer gas to a gap between the back surface of the substrate W and the central region 111a.

The shower head 13 is configured to introduce at least one processing gas from the gas supply unit 20 into the plasma processing space 10s. The shower head 13 has at least one gas supply port 13a, at least one gas diffusion chamber 13b, and multiple gas inlets 13c. The processing gas supplied to the gas supply port 13a passes through the gas diffusion chamber 13b and is introduced into the plasma processing space 10s from the multiple gas inlets 13c. The shower head 13 also includes at least one upper electrode. In addition to the shower head 13, the gas introduction unit may include one or more side gas injectors (SGIs) attached to one or more openings formed in the sidewall 10a.

The gas supply 20 may include at least one gas source 21 and at least one flow controller 22. In one embodiment, the gas supply 20 is configured to supply at least one process gas from a respective gas source 21 through a respective flow controller 22 to the showerhead 13. Each flow controller 22 may include, for example, a mass flow controller or a pressure-controlled flow controller. Additionally, the gas supply 20 may include at least one flow modulation device that modulates or pulses the flow rate of the at least one process gas.

The power supply 30 includes an RF power supply 31 coupled to the plasma processing chamber 10 via at least one impedance matching circuit. The RF power supply 31 is configured to supply at least one RF signal (RF power) to at least one lower electrode and/or at least one upper electrode. This causes a plasma to be formed from at least one processing gas supplied to the plasma processing space 10s. Thus, the RF power supply 31 can function as at least a part of the plasma generating unit 12. In addition, by supplying a bias RF signal to at least one lower electrode, a bias potential is generated on the substrate W, and ion components in the formed plasma can be attracted to the substrate W.

In one embodiment, the RF power supply 31 includes a first RF generating section 31a and a second RF generating section 31b. The first RF generating section 31a is coupled to at least one lower electrode and/or at least one upper electrode via at least one impedance matching circuit and configured to generate a source RF signal (source RF power) for plasma generation. In one embodiment, the source RF signal has a frequency in the range of 10 MHz to 150 MHz. In one embodiment, the first RF generating section 31a may be configured to generate multiple source RF signals having different frequencies. The generated one or more source RF signals are supplied to at least one lower electrode and/or at least one upper electrode.

The second RF generator 31b is coupled to at least one lower electrode via at least one impedance matching circuit and configured to generate a bias RF signal (bias RF power). The frequency of the bias RF signal may be the same as or different from the frequency of the source RF signal. In one embodiment, the bias RF signal has a lower frequency than the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency in the range of 100 kHz to 60 MHz. In one embodiment, the second RF generator 31b may be configured to generate multiple bias RF signals having different frequencies. The generated one or more bias RF signals are provided to at least one lower electrode. Also, in various embodiments, at least one of the source RF signal and the bias RF signal may be pulsed.

The power supply 30 may also include a DC power supply 32 coupled to the plasma processing chamber 10. The DC power supply 32 includes a first DC generator 32a and a second DC generator 32b. In one embodiment, the first DC generator 32a is connected to at least one lower electrode and configured to generate a first DC signal. The generated first DC signal is applied to the at least one lower electrode. In one embodiment, the second DC generator 32b is connected to at least one upper electrode and configured to generate a second DC signal. The generated second DC signal is applied to the at least one upper electrode.

In various embodiments, the first and second DC signals may be pulsed. In this case, a sequence of voltage pulses is applied to at least one lower electrode and/or at least one upper electrode. The voltage pulses may have a rectangular, trapezoidal, triangular, or combination thereof pulse waveform. In one embodiment, a waveform generator for generating a sequence of voltage pulses from the DC signal is connected between the first DC generator 32a and at least one lower electrode. Thus, the first DC generator 32a and the waveform generator constitute a voltage pulse generator. When the second DC generator 32b and the waveform generator constitute a voltage pulse generator, the voltage pulse generator is connected to at least one upper electrode. The voltage pulses may have a positive polarity or a negative polarity. Also, the sequence of voltage pulses may include one or more positive polarity voltage pulses and one or more negative polarity voltage pulses within one period. The first and second DC generating units 32a and 32b may be provided in addition to the RF power source 31, or the first DC generating unit 32a may be provided in place of the second RF generating unit 31b.

The exhaust system 40 may be connected to, for example, a gas exhaust port 10e provided at the bottom of the plasma processing chamber 10. The exhaust system 40 may include a pressure regulating valve and a vacuum pump. The pressure in the plasma processing space 10s is adjusted by the pressure regulating valve. The vacuum pump may include a turbomolecular pump, a dry pump, or a combination thereof.

Figure 3 is a flowchart of an etching method according to one exemplary embodiment. The etching method MT1 (hereinafter referred to as "method MT1") shown in Figure 3 can be performed by the plasma processing apparatus 1 of the above embodiment. Method MT1 can be applied to a substrate W.

Figure 4 is a cross-sectional view of an example substrate W to which the method of Figure 3 can be applied. As shown in Figure 4, in one embodiment, the substrate W comprises a film to be etched FL and a mask MK on the film to be etched FL. The substrate W may further comprise a base region UR below the film to be etched FL.

The film FL to be etched may include silicon (Si). The film FL to be etched may include silicon and nitrogen (N). The film FL to be etched may include at least one selected from the group consisting of a silicon nitride film (SiN film), a silicon oxynitride film (SiON film), and a laminated film. The laminated film may include a silicon oxide film and a silicon nitride film. The silicon oxide film and the silicon nitride film may be laminated alternately.

The mask MK may have an opening OP. The mask MK may have a plurality of openings OP. The opening OP may have a hole pattern or a line pattern. The dimension (CD: Critical Dimension) of the opening OP may be 100 nm or less. The mask MK may include a carbon-containing film or a metal-containing film. The carbon-containing film may include an amorphous carbon film. The metal-containing film may include at least one selected from the group consisting of tungsten silicide (WSi), tungsten carbide (WC), and titanium nitride (TiN).

The underlying region UR may include a silicon-containing film. The underlying region UR may include at least one film for a memory device, such as a DRAM or 3D-NAND.

Method MT1 will be described below with reference to Figs. 3 to 7, taking as an example a case where method MT1 is applied to a substrate W using the plasma processing apparatus 1 of the above embodiment. Each of Figs. 5 to 7 is a cross-sectional view showing one step of an etching method according to one exemplary embodiment. When the plasma processing apparatus 1 is used, method MT1 can be performed in the plasma processing apparatus 1 by controlling each part of the plasma processing apparatus 1 by the control unit 2. In method MT1, a substrate W on a substrate support 11 arranged in a plasma processing chamber 10 is processed, as shown in Fig. 2.

As shown in FIG. 3, method MT1 may include steps ST1 to ST5. Steps ST1 to ST5 may be performed in sequence. Step ST4 may be performed after step ST3, or may be performed simultaneously with step ST3. Steps ST2, ST3, and ST4 may be performed simultaneously. Steps ST1 to ST5 may be performed in-situ or in-system. Method MT1 may not include step ST5.

(Step ST1)
In step ST1, a substrate W shown in Fig. 4 is provided. The substrate W may be disposed in a plasma processing chamber 10. The substrate W may be supported by a substrate support 11 in the plasma processing chamber 10. The base region UR may be disposed between the substrate support 11 and the etching target film FL.

(Step ST2)
In step ST2, as shown in Fig. 5, the substrate W is etched to form a first portion RS1 of the recess RS in the substrate W. The etching target film FL may be etched through the opening OP by plasma generated from a processing gas. The etching may form the first portion RS1 of the recess RS in the etching target film FL. The first portion RS1 has a sidewall RSa and a bottom surface RSb. The bottom surface RSb may be separated from the underlying region UR.

When the etching target film FL contains silicon and nitrogen, a first processing gas may be used as the processing gas. In that case, in the process ST2, as shown in FIG. 5, the etching target film FL may be etched through the opening OP by a first plasma PL1 generated from the first processing gas. The first processing gas may contain hydrogen (H), fluorine (F), and boron (B). The first processing gas may contain a hydrogen-containing gas, a fluorine-containing gas, and a boron-containing gas. The hydrogen-containing gas may contain at least one selected from the group consisting of hydrogen gas ( _H2 gas), hydrogen fluoride gas ( _HF gas), and _{hydrofluorocarbon gas (CxHyFz gas} , where x, y, and z are natural numbers). The fluorine-containing gas may include at least one selected from the group consisting of hydrogen fluoride gas (HF gas), _fluorocarbon gas ( _CxFy gas, _{x and} y are natural numbers), hydrofluorocarbon gas ( _CxHyFz gas), nitrogen trifluoride gas ( _NF3 gas), phosphorus trifluoride gas ( _PF3 gas), and phosphorus pentafluoride gas ( _PF5 gas). The boron-containing gas may include at least one selected from the group consisting of boron trichloride gas ( _BCl3 gas), boron trifluoride gas ( _BF3 gas), boron hydride gas (e.g., _BH3 gas), and boron tribromide gas ( _BBr3 gas). The first process gas may not include nitrogen.

The first process gas may further include at least one additive gas selected from the group consisting of a phosphorus-containing gas, a halogen-containing gas, a nitrogen-containing gas, and an oxygen-containing gas. The phosphorus-containing gas may include at least one selected from the group consisting of phosphorus trifluoride gas ( _PF3 gas) and phosphorus pentafluoride gas ( _PF5 gas). The halogen-containing gas may include at least one selected from the group consisting of a chlorine-containing gas and a bromine-containing gas. The chlorine-containing gas may include _Cl2 gas. The bromine-containing gas may include HBr gas. The nitrogen-containing gas may include at least one selected from the group consisting of nitrogen gas ( _N2 gas), oxynitride gas (NO gas), nitrogen trifluoride gas ( _NF3 gas), ammonia gas ( _NH3 gas), a mixed gas of nitrogen gas and hydrogen gas, and an amine gas. The oxygen-containing gas may include at least one selected from the group consisting of oxygen gas ( _O2 ), carbon monoxide gas (CO), and carbon dioxide gas ( _CO2 ).

The recess RS may be provided in the film FL to be etched before the substrate W is supplied into the plasma processing chamber 10 (before step ST1). In that case, step ST2 may be omitted.

(Step ST3)
In step ST3, as shown in FIG. 6, an ammonium fluoroborate (hereinafter, referred to as "AFB") layer DP is formed on the sidewall RSa of the first portion RS1. The AFB layer DP may be formed by a first plasma PL1 generated from a first processing gas. The AFB may be generated by a reaction between a chemical species in the first plasma PL1 and the etching target film FL. The AFB layer DP may be formed in the sidewall RSa of the first portion RS1. Here, the case where the AFB layer DP is formed in the sidewall RSa means that the AFB layer DP is formed inside the sidewall RSa in the vicinity of the surface of the sidewall RSa. The step ST3 may be performed by exposing the substrate W (etching target film FL) to the first plasma PL1 generated from the first processing gas. The AFB layer DP may not be formed on the bottom surface RSb of the recess RS, or may be formed on the bottom surface RSb of the recess RS. The AFB layer DP may include ammonium tetrafluoroborate (NH ₄ BF ₄ ).

Step ST3 may be performed at a temperature of 50°C or less at the substrate support 11 that supports the substrate W. By performing step ST3 at a low temperature, AFB may be less likely to volatilize. In step ST3, the temperature of the substrate support 11 may be 30°C or less, 0°C or less, or -20°C or less. The temperature of the substrate support 11 may be -60°C or more. In step ST3, the temperature of the substrate W may be 60°C or less, or 200°C or less. The temperature of the substrate W may be 30°C or more. Since the temperature at which AFB decomposes is approximately 200°C, by having the temperature of the substrate W in step ST3 be 200°C or less, AFB may be less likely to volatilize.

(Step ST4)
In step ST4, as shown in Fig. 7, the bottom surface RSb is etched while the sidewall RSa is protected by the AFB layer DP. The bottom surface RSb can be etched by a first plasma PL1 generated from a first process gas. In step ST4, a second portion RS2 of the recess RS is formed below the first portion RS1. In step ST4, by protecting the sidewall RSa with the AFB layer DP, the intrusion of chemical species into the sidewall RSa can be prevented, and etching of the sidewall RSa can be suppressed.

The first process gas in step ST4 may be different from the first process gas in step ST3. The first process gas in step ST4 may not contain a boron-containing gas or may contain a boron-containing gas at a flow rate less than the flow rate of the boron-containing gas in the first process gas in step ST3.

(Step ST5)
In step ST5, steps 3 and 4 are repeated. The recesses RS become deeper by repeating steps 3 and 4. At the end of step ST5, the bottom surfaces RSb of the recesses RS may reach the underlying regions UR.

An example of the temperature of the substrate support part 11 in steps ST2, ST4, and ST5 may be the same as the example of the temperature of the substrate support part 11 in step ST3. An example of the temperature of the substrate W in steps ST2, ST4, and ST5 may be the same as the example of the temperature of the substrate W in step ST3.

In steps ST2 to ST5, a second processing gas may be used as the processing gas instead of the first processing gas. When the second processing gas is used, the method MT may be performed in the same manner as when the first processing gas is used, except for the following points. In step ST2, as shown in FIG. 5, the etching target film FL may be etched through the opening OP by a second plasma PL2 generated from the second processing gas. The second processing gas may contain nitrogen (N), hydrogen (H), fluorine (F), and boron (B). The second processing gas may contain a nitrogen-containing gas, a hydrogen-containing gas, a fluorine-containing gas, and a boron-containing gas. The nitrogen-containing gas may contain at least one selected from the group consisting of nitrogen gas (N ₂ gas), oxynitride gas (NO gas), nitrogen trifluoride gas (NF ₃ gas), ammonia gas (NH ₃ gas), a mixed gas of nitrogen gas and hydrogen gas, and an amine gas. When the second processing gas is used, the etching target film FL may contain silicon. The film to be etched FL may not contain nitrogen. The second process gas may further contain at least one additive gas selected from the group consisting of a phosphorus-containing gas, a halogen-containing gas, and an oxygen-containing gas. An example of the additive gas contained in the second process gas may be the same as the example of the additive gas contained in the first process gas. As shown in FIG. 6, the process ST3 may be performed by exposing the substrate W (film to be etched FL) to a second plasma PL2 generated from the second process gas. In the process ST4, as shown in FIG. 7, the bottom surface RSb may be etched by the second plasma PL2 generated from the second process gas while the sidewall RSa is protected by the AFB layer DP.

According to the above-described method MT1, the sidewall RSa is protected by the AFB layer DP, so that etching of the sidewall RSa is suppressed. This makes it possible to suppress shape abnormalities (e.g., bowing) of the recess RS.

Although various exemplary embodiments have been described above, various additions, omissions, substitutions, and modifications may be made without being limited to the exemplary embodiments described above. In addition, elements in different embodiments may be combined to form other embodiments.

Figure 8 is a flowchart of an etching method according to a first modified example (hereinafter referred to as "method MT2"). Figures 9 and 10 are cross-sectional views showing one step of the etching method according to the first modified example. Method MT2 may be performed in the same manner as method MT1, except for step ST3. Step ST3 of method MT2 includes steps ST31 and ST32. Step ST32 may be performed after step ST31.

(Step ST31)
In the step ST31, as shown in FIG. 9, an ammonium salt-containing layer DP1 not containing boron may be formed in or on the side wall RSa of the first portion RS1. The ammonium salt-containing layer DP1 may contain ammonium fluorosilicate (hereinafter referred to as "AFS"). The ammonium salt-containing layer DP1 may contain at least one selected from the group consisting of (NH ₄ ) ₂ SiF ₆ , NH ₄ SiF ₅ , and (NH ₄ ) ₃ SiF _7. The step ST31 may be performed by exposing the substrate W (film to be etched FL) to a third plasma PL3 generated from a third process gas containing hydrogen and fluorine. The third process gas may contain a hydrogen-containing gas and a fluorine-containing gas. When the third process gas is used, the film to be etched FL may contain silicon and nitrogen. The third process gas may not contain nitrogen. The third process gas may include at least one gas selected from the group consisting of a phosphorus-containing gas and a halogen-containing gas. The process ST31 may be performed by exposing the substrate W to a fifth plasma PL5 generated from a fifth process gas containing nitrogen, hydrogen, and fluorine. The fifth process gas may include a nitrogen-containing gas, a hydrogen-containing gas, and a fluorine-containing gas. When the fifth process gas is used, the film FL to be etched may include silicon. The film FL to be etched may not include nitrogen. The fifth process gas may include at least one gas selected from the group consisting of a phosphorus-containing gas and a halogen-containing gas. The AFB may be generated by a reaction between the chemical species in the third plasma PL3 or the fifth plasma PL5 and the film FL to be etched.

When the third process gas or the fifth process gas contains a phosphorus-containing gas, the ammonium salt-containing layer DP1 may contain ammonium hexafluorophosphate (NH ₄ PF ₆ ). When the third process gas or the fifth process gas contains a halogen-containing gas, the ammonium salt-containing layer DP1 may contain NH ₄ X (X is a halogen element). When the third process gas or the fifth process gas contains a bromine-containing gas, the ammonium salt-containing layer DP1 may contain ammonium bromide (NH ₄ Br).

(Step ST32)
In step ST32, as shown in FIG. 10, an AFB-containing layer DP2 is formed from the ammonium salt-containing layer DP1. The AFB-containing layer DP2 contains AFB. The AFB-containing layer DP2 may contain other than AFB. The AFB-containing layer DP2 may contain NH ₄ PF _6. When a third processing gas is used in step ST31, step ST32 may be performed by exposing the ammonium salt-containing layer DP1 to a fourth plasma PL4 generated from a fourth processing gas containing boron. The fourth processing gas may contain a boron-containing gas. The boron-containing gas may, for example, replace silicon in the ammonium salt-containing material that does not contain boron with boron through a reaction between the boron-containing gas and the ammonium salt-containing layer DP1. As a result, AFB may be generated. When the fifth process gas is used in step ST31, step ST32 may be performed by exposing the ammonium salt-containing layer DP1 to a sixth plasma PL6 generated from a sixth process gas containing boron. The sixth process gas may contain a boron-containing gas.

According to method MT2, by producing an AFB-containing material from an ammonium salt-containing material that does not contain boron, it is possible to suppress shape defects in the recesses RS caused by the ammonium salt-containing material that does not contain boron.

Figures 11 and 12 are flow charts of an etching method according to a second modified example (hereinafter, referred to as "method MT3"). Method MT3 has step ST6 instead of steps ST2 to ST5 of method MT1. In method MT3, in step ST1, as shown in FIG. 4, a substrate W having an etching target film FL containing silicon and nitrogen and a mask MK on the etching target film FL is provided. In step ST6, as shown in FIGS. 5 and 6, a recess RS is formed in the etching target film FL by plasma generated from a process gas containing hydrogen, fluorine, and boron, while an AFB layer DP is formed on the side wall RSa of the recess RS. As shown in FIG. 7, step ST6 also includes a step (step ST4 in method MT1) of etching the bottom surface RSb while protecting the side wall RSa with the AFB layer DP. Thus, in step ST6, steps ST2 to ST5 can be performed simultaneously.

As shown in FIG. 12, step ST6 may include steps ST61 to ST63. Steps ST61 to ST63 may be performed in sequence.

(Step ST61)
In step ST61, a first plasma PL1 is generated from a first process gas. The first process gas may include hydrogen and fluorine and may include a boron-containing gas at a first flow rate. In step ST61, formation of an AFB layer DP on a sidewall RSa of the recess RS may be promoted rather than etching of the bottom surface RSb.

(Step ST62)
In step ST62, a second plasma PL2 is generated from a second process gas. The second process gas may include hydrogen and fluorine. The second process gas may not include a boron-containing gas or may include a boron-containing gas at a second flow rate that is lower than the first flow rate. In step ST62, etching of the bottom surface RSb may be promoted rather than formation of the AFB layer DP.

(Step ST63)
In step ST63, steps ST61 and ST62 are repeated. By repeating steps ST61 and ST62, the recesses RS become deeper.

Various experiments conducted to evaluate Methods MT1, MT2, and MT3 are described below. The experiments described below do not limit the present disclosure.

Figure 13 is a partially enlarged cross-sectional view of an example substrate for evaluating the degree of shape defect of the recess RS. A recess RS is formed in the etching target film FL of the substrate W shown in Figure 5. The center reference line CL of the recess RS passes through the midpoint MP of the width of the recess RS at the upper end of the recess RS. By measuring the deviation of the midpoint MP from the center reference line CL along the depth direction of the recess RS, the degree of shape defect (twist or twist) of the recess RS can be evaluated.

(First Experiment)
In the first experiment, a substrate having the same structure as the substrate shown in FIG. 4 was prepared. The film to be etched was a laminated film including silicon oxide films and silicon nitride films alternately stacked. The film to be etched was then etched by plasma generated from a processing gas. The processing gas was a mixed gas including 90% by volume of a fluorine-containing gas, oxygen gas, hydrogen bromide gas, and 2% by volume of BCl ₃ gas. In this specification, each volume percentage indicates the ratio of the flow rate (unit: sccm) of each gas to the total flow rate (unit: sccm) of the processing gas. The temperature of the substrate support during etching was −50° C. or lower.

(Second Experiment)
In the second experiment, the target film was etched in the same manner as in the first experiment, except that the processing gas was different. In the second experiment, the processing gas was a mixed gas containing 92% by volume of a fluorine-containing gas and an oxygen-containing gas. The processing gas did not contain hydrogen bromide gas or BCl ₃ gas.

(Experimental Results)
In each of the first and second experiments, after etching of the film to be etched, a surface analysis of the sidewall RSa of the recess RS was performed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). As a result, in the first experiment, AFB was detected, but AFS was not detected. In the second experiment, AFS was detected, but AFB was not detected.

After etching the film to be etched in each of the first and second experiments, the deviation of the midpoint MP of the width of the recess RS from the center reference line CL was obtained in the cross section of the substrate along the depth direction of the recess RS, as shown in FIG. 13. FIG. 14 is a graph showing an example of an experiment result evaluating the degree of shape abnormality of the recess. The horizontal axis of the graph indicates the deviation (nm) of the midpoint MP of the width of the recess RS from the center reference line CL. The vertical axis of the graph indicates the depth (nm) of the recess RS. The position where the depth of the recess RS is 0 corresponds to the boundary between the mask and the film to be etched. The maximum deviation (about 45 nm) of the profile E2 showing the deviation of the midpoint MP in the second experiment was larger than the maximum deviation (about 30 nm) of the profile E1 showing the deviation of the midpoint MP in the first experiment. Therefore, it was found that the degree of shape abnormality of the recess RS can be improved when the processing gas contains hydrogen and boron. It is assumed that the formation of an AFB layer on or within the sidewall RSa of the recess RS has improved the degree of shape defects of the recess RS.

After etching the film to be etched in each of the first and second experiments, the cross-sectional shape of the recess RS near the bottom surface RSb was observed as shown in Figures 15 and 16. The cross section of the recess RS is a cross section perpendicular to the depth direction of the recess RS. In the cross section, the recess RS has a line pattern. Figure 15 shows the results of the first experiment, and Figure 16 shows the results of the second experiment. In each of the first and second experiments, the width of the recess RS (CD: Critical Dimension) was measured. The width of the recess RS in the first experiment was 56.7 nm. The width of the recess RS in the second experiment was 104 nm. Therefore, it was found that the width of the recess RS is reduced when the processing gas contains hydrogen and boron.

In each of the first and second experiments, the line edge roughness (LER) of the recess RS was measured from the cross section of the recess RS. LER is, for example, the arithmetic mean roughness measured along the sidewall RSa of the recess RS. The LER in the first experiment was 28 nm. The LER in the second experiment was 33 nm. Therefore, it was found that the LER is improved when the process gas contains hydrogen and boron.

Experiments were also conducted in the same manner as in the first and second experiments for the case where the recess RS had a hole pattern. As a result, it was found that by adding BCl ₃ gas to the processing gas used for plasma etching, an AFB layer was formed on or within the sidewall RSa of the recess RS, and the degree of shape defects of the recess RS was improved. Specifically, the maximum bowing width was 101 nm when BCl ₃ was not added, but improved to 99 nm when BCl ₃ was added. The width of the recess RS was 29 nm when BCl ₃ was not added, but improved to 20 nm when BCl ₃ was added.

Various exemplary embodiments included in this disclosure are described below in [E1] to [E20].

[E1]
(a) etching a substrate to form a first portion of a recess in the substrate, the first portion including a bottom surface and a sidewall;
(b) forming an ammonium fluoroborate layer in or on said sidewalls;
(c) etching the bottom surface while protecting the sidewalls with the ammonium fluoroborate layer to form a second portion of the recess below the first portion;
An etching method comprising:

[E2]
The etching method according to [E1], wherein the step (b) is carried out at a temperature of a substrate support part supporting the substrate of 50° C. or less.

[E3]
The etching method according to [E1] or [E2], wherein (c) is carried out after (b).

[E4]
(d) The etching method according to any one of [E1] to [E3], further comprising the step of repeating the steps (b) and (c).

[E5]
The etching method according to [E1] or [E2], wherein (a), (b) and (c) are carried out simultaneously.

[E6]
the substrate includes a film to be etched;
the film to be etched includes silicon and nitrogen;
(b) is performed by exposing the substrate to a first plasma generated from a first process gas;
The etching method according to any one of [E1] to [E5], wherein the first process gas contains hydrogen, fluorine, and boron.

[E7]
The etching method according to [E6], wherein the etching target film includes at least one selected from the group consisting of a silicon nitride film, a silicon oxynitride film, and a laminated film, and the laminated film includes a silicon oxide film and a silicon nitride film.

[E8]
The etching method according to [E6] or [E7], wherein the first process gas contains a hydrogen-containing gas, a fluorine-containing gas, and a boron-containing gas.

[E9]
The etching method according to any one of [E6] to [E8], wherein the first process gas further contains at least one additive gas selected from the group consisting of a phosphorus-containing gas, a halogen-containing gas, a nitrogen-containing gas, and an oxygen-containing gas.

[E10]
the substrate includes a film to be etched;
the film to be etched includes silicon;
(b) is performed by exposing the substrate to a second plasma generated from a second process gas;
The etching method according to any one of [E1] to [E5], wherein the second process gas contains nitrogen, hydrogen, fluorine, and boron.

[E11]
The etching method according to [E10], wherein the second process gas contains a nitrogen-containing gas, a hydrogen-containing gas, a fluorine-containing gas, and a boron-containing gas.

[E12]
The etching method according to [E10] or [E11], wherein the second process gas further contains at least one additive gas selected from the group consisting of a phosphorus-containing gas, a halogen-containing gas, and an oxygen-containing gas.

[E13]
The etching method according to any one of [E1] to [E12], wherein the substrate includes a mask, and the mask includes a carbon-containing film or a metal-containing film.

[E14]
The (b) is
(b1) forming a boron-free ammonium salt-containing layer in or on the sidewall;
(b2) producing an ammonium fluoroborate-containing layer containing ammonium fluoroborate from the boron-free ammonium salt-containing layer;
The etching method according to any one of [E1] to [E13],

[E15]
the substrate includes a film to be etched;
the film to be etched includes silicon and nitrogen;
(b1) is performed by exposing the substrate to a third plasma generated from a third process gas comprising hydrogen and fluorine;
The etching method according to [E14], wherein (b2) is carried out by exposing the boron-free ammonium salt-containing layer to a fourth plasma generated from a fourth process gas containing boron.

[E16]
the substrate includes a film to be etched;
the film to be etched includes silicon;
(b1) is performed by exposing the substrate to a fifth plasma generated from a fifth process gas comprising nitrogen, hydrogen, and fluorine;
The etching method according to [E14], wherein (b2) is carried out by exposing the boron-free ammonium salt-containing layer to a sixth plasma generated from a sixth process gas containing boron.

[E17]
(a) providing a substrate having a film to be etched comprising silicon and nitrogen and a mask on the film to be etched;
(b) forming a recess in the film to be etched by plasma generated from a process gas containing hydrogen, fluorine, and boron while forming an ammonium fluoroborate layer on a side wall of the recess;
An etching method comprising:

[E18]
The (b) is
(b1) generating a first plasma from a first process gas, the first process gas including hydrogen and fluorine and including a boron-containing gas at a first flow rate;
(b2) generating a second plasma from a second process gas, the second process gas containing hydrogen and fluorine, and the second process gas not containing the boron-containing gas or containing the boron-containing gas at a second flow rate that is less than the first flow rate. The etching method according to [E17],

[E19]
The etching method according to [E18], wherein the (b) further includes a step (b3) of repeating the (b1) and the (b2).

[E20]
An etching apparatus comprising:
A chamber;
a substrate support for supporting a substrate within the chamber;
A control unit;
Equipped with
The control unit is
Etching the substrate to form a first portion of a recess in the substrate;
forming an ammonium fluoroborate layer in or on a sidewall of the first portion;
an etching apparatus configured to control the etching apparatus to etch a bottom surface of the first portion while protecting the sidewalls with the ammonium fluoroborate layer to form a second portion of the recess below the first portion.

1...plasma processing apparatus, 2...control unit, 10...plasma processing chamber, DP...ammonium fluoroborate layer (AFB layer), FL...film to be etched, MK...mask, RS...recess, RS1...first portion, RS2...second portion, RSa...side wall, RSb...bottom surface, W...substrate.

Claims (20)

(a) etching a substrate to form a first portion of a recess in the substrate, the first portion including a bottom surface and a sidewall;
(b) forming an ammonium fluoroborate layer in or on said sidewalls;
(c) etching the bottom surface while protecting the sidewalls with the ammonium fluoroborate layer to form a second portion of the recess below the first portion;
An etching method comprising: The etching method according to claim 1, wherein (b) is performed when the temperature of the substrate support part that supports the substrate is 50°C or less. The etching method according to claim 1 or 2, wherein (c) is performed after (b). The etching method of claim 3, further comprising the steps of (d) repeating (b) and (c). The etching method according to claim 1 or 2, wherein (a), (b) and (c) are carried out simultaneously. the substrate includes a film to be etched;
the film to be etched includes silicon and nitrogen;
(b) is performed by exposing the substrate to a first plasma generated from a first process gas;
3. The etching method of claim 1, wherein the first process gas contains hydrogen, fluorine, and boron. The etching method according to claim 6, wherein the film to be etched includes at least one selected from the group consisting of a silicon nitride film, a silicon oxynitride film, and a laminated film, and the laminated film includes a silicon oxide film and a silicon nitride film. The etching method of claim 6, wherein the first process gas includes a hydrogen-containing gas, a fluorine-containing gas, and a boron-containing gas. The etching method according to claim 8, wherein the first process gas further includes at least one additive gas selected from the group consisting of a phosphorus-containing gas, a halogen-containing gas, a nitrogen-containing gas, and an oxygen-containing gas. the substrate includes a film to be etched;
the film to be etched includes silicon;
(b) is performed by exposing the substrate to a second plasma generated from a second process gas;
3. The etching method of claim 1, wherein the second process gas contains nitrogen, hydrogen, fluorine, and boron. The etching method of claim 10, wherein the second process gas includes a nitrogen-containing gas, a hydrogen-containing gas, a fluorine-containing gas, and a boron-containing gas. The etching method according to claim 11, wherein the second process gas further includes at least one additive gas selected from the group consisting of a phosphorus-containing gas, a halogen-containing gas, and an oxygen-containing gas. The etching method according to claim 1 or 2, wherein the substrate includes a mask, and the mask includes a carbon-containing film or a metal-containing film. The (b) is
(b1) forming a boron-free ammonium salt-containing layer in or on the sidewall;
(b2) producing an ammonium fluoroborate-containing layer containing ammonium fluoroborate from the boron-free ammonium salt-containing layer;
The etching method according to claim 1 or 2, comprising: the substrate includes a film to be etched;
the film to be etched includes silicon and nitrogen;
(b1) is performed by exposing the substrate to a third plasma generated from a third process gas comprising hydrogen and fluorine;
15. The etching method of claim 14, wherein (b2) is performed by exposing the boron-free ammonium salt-containing layer to a fourth plasma generated from a fourth process gas that includes boron. the substrate includes a film to be etched;
the film to be etched includes silicon;
(b1) is performed by exposing the substrate to a fifth plasma generated from a fifth process gas comprising nitrogen, hydrogen, and fluorine;
15. The etching method of claim 14, wherein (b2) is performed by exposing the boron-free ammonium salt-containing layer to a sixth plasma generated from a sixth process gas that includes boron. (a) providing a substrate having a film to be etched comprising silicon and nitrogen and a mask on the film to be etched;
(b) forming a recess in the film to be etched by plasma generated from a process gas containing hydrogen, fluorine, and boron while forming an ammonium fluoroborate layer on a side wall of the recess;
An etching method comprising: The (b) is
(b1) generating a first plasma from a first process gas, the first process gas including hydrogen and fluorine and including a boron-containing gas at a first flow rate;
(b2) generating a second plasma from a second process gas, the second process gas including hydrogen and fluorine, the second process gas including no boron-containing gas or including the boron-containing gas at a second flow rate less than the first flow rate;
20. The etching method of claim 17, comprising: The etching method according to claim 18, further comprising the step of (b3) repeating the steps (b1) and (b2). An etching apparatus comprising:
A chamber;
a substrate support for supporting a substrate within the chamber;
A control unit;
Equipped with
The control unit is
Etching the substrate to form a first portion of a recess in the substrate;
forming an ammonium fluoroborate layer in or on a sidewall of the first portion;
an etching apparatus configured to control the etching apparatus to etch a bottom surface of the first portion while protecting the sidewalls with the ammonium fluoroborate layer to form a second portion of the recess below the first portion.

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